**Core Concept**
Shepherd's crook deformity of the proximal femur is a characteristic radiological finding associated with a specific condition affecting bone health. It is characterized by a varus angulation of the proximal femur, giving it a crook-like appearance on radiographs.

**Why the Correct Answer is Right**
The shepherd's crook deformity is a hallmark feature of Fibrous Dysplasia, a non-neoplastic bone disorder that leads to the replacement of normal bone with fibrous tissue. This results in weakened bones that are prone to fractures and deformities. The varus angulation of the proximal femur occurs due to the abnormal growth of fibrous tissue, which disrupts the normal architecture of the bone. The affected bone often becomes thinned and cortical, making it more susceptible to fractures.

**Why Each Wrong Option is Incorrect**
* **Option A:** Fibrous Dysplasia is not typically associated with osteoarthritis, which is a degenerative joint disease characterized by cartilage loss and bone-on-bone contact.
* **Option B:** Osteogenesis Imperfecta, also known as brittle bone disease, is a genetic disorder that affects collagen production, leading to fragile bones. However, it is not typically characterized by a shepherd's crook deformity.
* **Option C:** Rickets is a disease caused by vitamin D deficiency, leading to softening of bones in children. It does not typically result in a shepherd's crook deformity.

**Clinical Pearl / High-Yield Fact**
Fibrous Dysplasia often presents with a triad of symptoms: pain, deformity, and fractures. It is essential to recognize the characteristic radiological features, including the shepherd's crook deformity, to make an accurate diagnosis.

**Correct Answer:** D. Fibrous Dysplasia